This invention relates to rosin esters, and adhesives containing the rosin esters.
Esters of rosin and polyhydric alcohols (polyols), which are generally called rosin esters, have been known for over 70 years. See, e.g., U.S. Pat. No. 1,696,337 to Symmes. They are typically prepared by the reaction of rosin (a mixture of isomeric C20 tricyclic mono-carboxylic acids) with polyhydric alcohols (hereinafter xe2x80x9cpolyolsxe2x80x9d) such as pentaerythritol. Rosin esters currently find widespread commercial use in many applications, including as tackifiers for packaging and pressure-sensitive adhesives, and in cosmetic formulations.
For many applications, the color of a rosin ester is a property which determines its commercial viability. Rosin ester coloration is typically measured on the Gardner color scale, with a Gardner color of zero being colorless, and a color of fifteen being red-brown. The marketplace places a premium on rosin esters that are light in color, and will not accept very darkly colored esters. However, light-colored rosin esters are difficult and/or expensive to prepare and maintain. A considerable amount of research has been directed at producing rosin esters that are both initially light-colored, and will maintain this light coloration upon prolonged storage and/or during a heating process to which the ester may be subjected during its formulation into a specific final product. See, e.g., U.S. Pat. Nos. 2,409,173 to Webb; 3,423,389 to Glenn and 5,395,920 to Maeda et al., which are representative only. The ""920 patent to Maeda et al. discloses that it is possible (although, in practice, probably cost-prohibitive) to make a rosin ester having a Gardner color of not more than one, through extensive purification, disproportionation and dehydrogenation of the starting rosin and/or final rosin ester.
Despite a significant amount of research, there remains a need in the art for cost-effective methods to achieve light-colored rosin esters. The present invention fulfills this need and provides related advantages as described herein.
In one aspect, the present invention provides a light-colored esterification product of rosin and an aromatic or aliphatic hydrocarbon moiety containing at least two hydroxyl groups, with the proviso that the hydroxyl groups are separated in the moiety by at least four carbon atoms. In preferred embodiments, the product has undergone disproportionation, has not undergone dehydrogenation, has a color of Gardner value of less than 2.5, includes a stabilizer such as an antioxidant or UV stabilizer, and/or is prepared from a starting rosin having a color of Gardner value of at least 3.
Another aspect of the present invention provides an adhesive composition that includes polymer and, as a modifier thereof, the light-colored esterification product of rosin and an aromatic or aliphatic hydrocarbon moiety containing at least two hydroxyl groups, as described above.
These and other aspects of this invention will become apparent upon reference to the following detailed description. To this end, certain references are cited herein for purpose of clarity and completeness. Such references are incorporated herein by reference in their entirety.
The present invention is directed to the esterification products of rosin and aromatic or aliphatic hydrocarbon moieties containing at least two hydroxyl groups. The invention is also directed to adhesive compositions containing these rosin esters. It has been surprisingly discovered that when rosin esters have ester groups separated by at least four carbon atoms, the esters have remarkably light color, and remarkably good performance properties as tackifiers in adhesive formulations.
Rosin is mainly a mixture of C20, tricyclic fused-ring, monocarboxylic acids, typified by pimaric and abietic acids, which are commonly referred to as xe2x80x9cresin acids.xe2x80x9d Rosin which is suitable for use in the present invention can be obtained from many sources, and can have a wide range of purities. For example, wood rosin may be employed in the present invention, where wood rosin is obtained from Pinus stumps after harvesting the stumps, chipping the stumps into small chips, extracting the chips with hexane or higher-boiling paraffins, and distilling the hexane or paraffin to yield wood rosin. Gum rosin, which is the name given to rosin that is obtained after scoring a pine tree, collecting the exudate sap, and then distilling away the volatile components, may also be employed in the invention.
The rosin may be tall oil rosin, which is a by-product of the kraft (i.e., sulfate) pulping process for making paper. According to this process, pinewood is digested with alkali and sulfide, producing tall oil soap and crude sulfate turpentine as by-products. Acidification of this soap followed by fractionation of the crude tall oil yields tall oil rosin and fatty acids. Any one or more of the C20 cyclic carboxylic acid-containing isomers present in rosin may be used in the invention.
Regardless of its source, rosin is typically characterized by its acid number, and rosins having acid numbers ranging from about 160 to about 195 are preferred according to the invention. Rosin may also be characterized by its Gardner color, where lower Gardner color numbers indicate lighter-colored rosin. Light-colored rosin is preferred for preparation of tackifiers. However, in order for the present invention to have commercial viability, the rosin is preferably not subjected to extensive purifying or modifying processes, which will necessarily add cost to the process for making the rosin ester. Thus, in a preferred embodiment, the rosin is xe2x80x9cstandardxe2x80x9d grade rosin as is readily available from many commercial distillers of naval stores. This standard grade rosin has not be subjected to disproportionation or dehydrogenation processes prior to its use in the esterification reaction of the present invention. Furthermore, the standard grade of rosin has also not undergone any special purification procedures such as redistillation (i.e., further distillation of rosin after it has already been isolated by distillation from crude tall oil), recrystallization or extraction procedures to remove impurities. Instead, the preferred rosin of the present invention is the standard grade of rosin that is produced upon distillation of crude tall oil, and is available from many sources. Such xe2x80x9cstandard gradexe2x80x9d rosin has a color of Gardner value of at least 3, more typically of at least 4, and still more typically of at least 5. In one embodiment, the present invention provides rosin esters having a color that is at least as light as the color of the rosin charged to the esterification reaction vessel, and typically provides rosin esters which are lighter in color than the starting rosin by at least one, at least one and a half, or at least two Gardner value units.
A significant advantage of the present invention is that it provides light-colored and low odor rosin esters from standard grade rosin. Of course, if desired, a purified rosin could also be employed in the present invention. If dehydrogenated rosin would be used in the invention, and the rosin is from crude tall oil, then the tall oil rosin will require substantially higher catalyst levels to achieve dehydrogenation (compared to, e.g., a gum or wood rosin) in order for all of the catalyst not to be deactivated by the sulfur bodies that are present in tall oil rosin.
A preferred standard grade of rosin is available commercially from Union Camp Corporation (Wayne, N.J.) under the UNI-TOL(copyright) trademark. Gum rosin, including Indonesian and Chinese gum rosins, is another suitable rosin for preparing rosin esters of the invention, where gum rosin may afford higher melting point rosin esters than can be obtained from using an equivalent amount of tall oil rosin, although may not provide the lightness in color that may be obtained from tall oil rosin.
The esterification product of the invention is prepared from rosin as described above and a polyol, where the polyol is an aromatic or aliphatic hydrocarbon moiety containing at least two hydroxyl groups, where those hydroxyl groups are separated from one another by at least four carbon atoms. As used herein, the hydrocarbon moiety consists solely of hydrogen and carbon, and may be either aromatic or aliphatic. The hydrocarbon may be cyclic (where the cyclic hydrocarbon may be either aromatic or aliphatic) or acyclic, where the acyclic hydrocarbon is aliphatic and may be either linear or branched, saturated or unsaturated, or any combination thereof. Aromatic refers to any conjugated cyclic polyene containing (4n+2) pi electrons, with n=1, 2, 3, etc. A saturated hydrocarbon does not contain any double or triple carbon-carbon bonds, i.e., is incapable of absorbing substances by addition. An unsaturated hydrocarbon contains at least one carbon-carbon double bond or contains at least one carbon-carbon triple bond.
As stated above, the aromatic or aliphatic hydrocarbon moiety contains at least two hydroxyl groups. Additionally, all of the hydroxyl groups are separated from each other by at least four carbon atoms, and in one embodiment of the invention are separated from each other by at least six carbon atoms. When the hydrocarbon moiety is cyclic, more than one path of carbon atoms may be observed to separate any two hydroxyl groups. In such a situation, it is necessary to count the fewest number of carbon atoms which separate two hydroxyl groups, and that fewest number must be four or greater in order for the hydrocarbon moiety to provide an esterification product of the present invention.
The present invention is directed to the surprising discovery that unexpectedly light colored rosin esters may be prepared from polyols having at least two hydoxyl groups, where all of the hydroxyl groups are separated from one another by at least four carbon atoms, and in one embodiment of the invention are separated from one another by at least six carbon atoms. The hydrocarbon moiety of the polyol used to prepare the esterification product necessarily contains at least four carbon atoms, and in one embodiment of the invention, contains at least six carbon atoms. Accordingly, 1,4-butanediol, which contains exactly four carbon atoms, is the smallest polyol that may be used in the present invention. The polyol may contain as many as about 40 carbon atoms. A preferred polyol is known as dimer diol, contains 36 carbon atoms, and is the reduction product of dimer acid. Dimer diol is commercially available from, e.g., Unichema International, Chicago, Ill. as PRIPLAS(trademark) 2033.
In one embodiment, the polyol contains from four to ten carbon atoms. Suitable polyols having carbon numbers falling within this range include 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol and 1,10-decanediol. Another polyol having 4-10 carbon atoms is 1,4-cyclohexanedimethanol, which has the Chemical Abstract Registry Number 105-08-8. 1,4-Cyclohexanedimethanol and other C4-C10 polyols are available from, for example, Aldrich Chemical Co. (Milwaukee, Wis.).
The polyol may contain an aromatic ring. For example, a suitable polyol for preparing an esterification product of the invention is 1,4-(CH2OH)2Ar, where Ar represents a benzene nucleus and the two methylol groups (CH2OH)2 are disposed in a para relationship around the benzene nucleus.
In a p referred embodiment, either the starting rosin or the esterification product thereof has undergone disproportionation to provide the product of the invention. Disproportionation is readily achieved by known disproportionation catalysts that are commonly used in the rosin esterification art. Exemplary disproportionation catalysts include, but are not limited to, supported metal catalysts such as rhodium on carbon, platinum on carbon, and palladium on carbon. Metal powder may also serve as a disproportionation catalyst, where exemplary metal powders include, but are not limited to, platinum, nickel, iodide and metal iodides such as iron iodide. These disproportionation catalysts are readily available from many commercial suppliers, for example, Aldrich Chemical Co. (Milwaukee, Wis.). They are typically used at a concentration of 0.01-5% by weight compared to the total weight of the rosin and polyol, and are preferably used at a concentration of 0.01 to 1% by weight.
A preferred disproportionation catalyst is a phenol sulfide compound. A preferred phenol sulfide compound has the formula 
where the Aryl group can be phenyl or naphthyl, R1, R2 and R3 can be the same or different and are hydrocarbon (also known as hydrocarbyl) groups, where xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d are independently 0, 1 or 2, and where xe2x80x9ccxe2x80x9d is an integer between 0 and 20. A preferred phenol sulfide compound is an amylphenol disulfide polymer (CAS Registry No. 68555-98-6), where such a polymer is available from Elf Atochem North America, Inc., Philadelphia, Pa., as VULTAC(trademark) 2. Typically, the amylphenol disulfide polymer is added to the rosin and polyol at a concentration of about 0.05 wt % to about 0.5 wt %, based on the total weight of rosin and polyol. Preferably, the phenol sulfide compound is added to the molten rosin prior to beginning the esterification reaction, although it can be added at a later stage. The phenol sulfide compound is believed to afford oxidative stability to the rosin ester, as well as some bleaching during formation of the rosin ester.
The light-colored esterification product (i.e., rosin ester) of the present invention preferably has not been subjected to dehydrogenation. Dehydrogenation refers to the removal of hydrogen from the rosin ester without replacement of another atom. The removal of hydrogen, without the concomitant addition of another atom, results in the formation of a carbon-carbon double bond from a carbon-carbon single bond. Dehydrogenation results when rosin or a rosin ester is exposed to a dehydrogenation catalyst at elevated temperature.
Although the rosin used to form the rosin ester of the present invention is preferably of xe2x80x9cstandard grade,xe2x80x9d the rosin may become stabilized in situ during the esterification reaction. As used herein, xe2x80x9cstabilizationxe2x80x9d refers to chemical modification of the rosin, or rosin moiety in the rosin ester, which imparts enhanced thermal or oxidation stability to the resulting rosin ester. Examples of stabilization include disproportionation, hydrogenation and dehydrogenation. As stated above, the rosin esterification product of the present invention preferably undergoes disproportionation but preferably does not undergo an additional dehydrogenation or hydrogenation.
One or more of various additives and catalysts may be present during the rosin esterification reaction. One useful additive is a metal salt, such as a calcium or magnesium salt, of a hindered phenylphosphonate or diphenylphosphonate (hereinafter xe2x80x9cphosphonate saltxe2x80x9d), which may be added to the reactants (rosin and polyol). These phosphonates are described, for example, in U.S. Pat. No. 3,310,575. A preferred phosphonate salt is calcium bismonoethyl(3,5-di-tert-butyl-4-hydroxy-benzyl)phosphonate (65140-91-2), commercially available from Ciba Specialty Chemicals (Tarrytown, N.Y.) as IRGANOX(trademark) 1425. Approximately 0.1 wt % to about 0.5 wt %, and preferably about 0.15 wt % to about 0.25 wt % of phosphonate salt may be added to the reactants, where the wt % values here and throughout this disclosure are based on the combined weight of rosin and polyol added to the reaction vessel.
Another useful phosphorus-containing additive has the formula (Rxe2x80x94Oxe2x80x94)3xe2x80x94P, where R is independently a C1-C22 hydrocarbyl radical. Exemplary phosphorous-containing additives of this general formula include, without limitation, phosphite compounds such as triphenylphosphite, tris(nonylphenyl)phosphite, phenyldiisodecylphosphite and the like. Phosphinic acid is another useful additive and is represented by the formula H2P(O)OH, where phosphinic acid is commercially available. Phosphoric acid is another useful additive. Such phosphorous-containing additives are typically employed at a concentration of 0.01-1 wt % based on the total weight of rosin and polyol. Phosphorous-containing materials, optionally in combination with VULTAC(trademark) 2, may be used to catalyze an esterification reaction of the present invention.
In one embodiment of the present invention, the esterification product has the following formula 
wherein R represents an aliphatic or aromatic hydrocarbon moiety having from 4 to 36 carbon atoms and xe2x80x9crosinxe2x80x9d represents the radical of a resin acid (e.g., abietic acid or a stabilized form thereof) that remains following removal of the carboxylic acid that is characteristic of a resin acid. In a further embodiment, R is an aliphatic hydrocarbon moiety having from 4 to 10 carbon atoms. The aliphatic hydrocarbon may be cyclic or acyclic, where the acyclic moiety may be linear or branched, and the moiety may contain both cyclic and acyclic portions. This esterification product is conveniently made from rosin and a dihydric polyol (i.e., a diol, having exactly two hydroxyl groups) having 4 to 36 carbon atoms. In another embodiment, a trihydric polyol (i.e., a triol, having exactly three hydroxyl groups) such as 1,3,5-benzenetrimethanol, 1,2,4-benzenetrimethanol, 1,3,5-cyclohexanetrimethanol and 1,2,4-cyclohexanetrimethanol, may be used.
In another embodiment, the esterification product has the following formula 
wherein xe2x80x9cRxe2x80x9d is a specific C8 cycloaliphatic moiety. This esterification product is conveniently prepared from 1,4-cyclohexanedimethanol and rosin.
The present invention provides light-colored rosin esters, that are preferably prepared from standard grade (i.e., not purified) rosin. In one embodiment, the esterification product (i.e., rosin ester) has a color of Gardner value of less than 2.5. In a further embodiment, the esterification product has a color of Gardner value between 0.5 and less than 2.5. In a further embodiment, the esterification product has a Gardner value of less than 2.0, and in a further embodiment, has a Gardner value of between 0.5 and less that 2.0.
In one embodiment, the present invention provides for an adhesive composition comprising a polymer and, as a modifier thereof, the rosin esterification product of rosin and an aromatic or aliphatic hydrocarbon moiety containing at least two hydroxyl groups as described above. The polymer may also be referred to as an elastomer or adhesive polymer component. The polymer should be an adhesively-suitable polymer, in that it may be formulated with the rosin ester of the present invention so as to provide a composition having adhesive properties. Polymers recognized in the art as suitable for the preparation of adhesives are suitable polymers for the adhesive compositions of the present invention.
Suitable adhesive polymers include, without limitation, isoprene-based block copolymers, butadiene-based block copolymers, hydrogenated block copolymers, ethylene vinyl acetate copolymer, polyester, polyester-based copolymers, neoprene, urethane, poly(acrylate), acrylate copolymers such as ethylene acrylic acid copolymer, ethylene n-butyl acrylate copolymer, and ethylene methyl acrylate copolymer, polyether ether ketone, polyamide, styrenic block copolymers, hydrogenated styrenic block copolymers, random styrenic copolymers, ethylene-propylene rubber, ethylene propylene rubber, butyl rubber, styrene butadiene rubbers, butadiene acrylonitrile rubber, polyester copolymers, natural rubber, polyisoprene, polyisobutylene, polyvinylacetate, polyolefin such as polyethylene and polypropylene including atactic polypropylene, and a terpolymer formed from the monomers ethylene, propylene, and a diene (EPDM).
Preferred polymers of the adhesive compositions of the invention include, without limitation, ethylene vinyl acetate copolymer, ethylene n-butyl acrylate copolymer, ethylene methyl acrylate copolymer, polyester, neoprene, urethane, poly(acrylate), ethylene acrylic acid copolymer, polyether ether ketone, polyamide, styrenic block copolymers, hydrogenated styrenic block copolymers, styrene butadiene copolymers, atactic polypropylene, polyethylene, ethylene-propylene rubber, butyl rubber, polyester copolymers, natural rubber, polyester, isoprene, and EPDM. Typically, a preferred polymer of the adhesive compositions of the invention is compatible with the rosin ester of the invention, where compatibility is demonstrated by a mixture of polymer and rosin ester being transparent, rather than opaque.
Typically, the adhesive composition will contain significant amounts of both rosin ester and polymer. For example, per 100 parts of rosin ester, the adhesive composition may contain 50 to 300 parts of polymer.
The adhesive compositions may additionally contain additives that render the composition particularly suitable for a particular application. The use of many such additives is well known in the art, and they may be used for their intended purpose in the adhesive compositions of the present invention. For example, if the adhesive is intended to serve as a hot melt packaging adhesive, then a wax is a useful additional ingredient. Suitable waxes include, without limitation, microcrystalline wax, paraffin wax, waxes produced by Fischer-Tropsch processes, vegetable wax and the like. Normally, a wax will be included in the composition in an amount of between 40 and 100 parts wax per 100 parts of the polymer component.
If the adhesive is intended for a pressure sensitive adhesive (PSA), then oil may be a useful ingredient. Suitable oils include naphthenic oil, paraffinic oils, mineral oils, triglyceride oils and the like. One or more plasticizers may be added to the composition, where suitable plasticizers include, without limitation, esters such as dibutyl phthalate and.dioctyl phthalate, chlorinated paraffins. One or more fillers, such as carbon black, titanium oxide and zinc oxide. Extender oils may be present in the composition, where exemplary extender oils include, without limitation, liquid paraffin, castor oil, rape seed oil, mineral oil, and the like.
Other resins may be present in the adhesive composition, where suitable resins include, without limitation, cycloaliphatic hydrocarbon resins, C5 hydrocarbon resins, C5/C9 hydrocarbon resins, C9 hydrocarbon resins, fully or partially hydrogenated hydrocarbon resins, terpene resins, modified terpene resins (terpene phenol or styrenated terpene), liquid resins, other rosin esters, and the like.
Thus, adhesives compositions of the present invention may include, in addition to polymer and one or more rosin esters of the invention, an additive selected from wax, process oil, cycloaliphatic hydrocarbon resin, C5 hydrocarbon resin, C5-C9 hydrocarbon resin, C9 hydrocarbon resin, terpene resin, terpene phenolic resin, terpene styrene resin, and esters of rosin and polyols characterized in that the hydroxyl groups thereof are separated by fewer than four carbon atoms.
The adhesive composition of the present invention may be prepared from the rosin ester, adhesive polymer and additional ingredients as described above, using conventional techniques and equipment. For example, the components of the adhesive composition may be blended in a mixer such as a Sigma blade mixer, a twin screw extruder or the like. The adhesive composition may be shaped into a desired form, such as a tape or sheet, by an appropriate technique including extrusion, compression molding, calendaring or the like.
The adhesive composition may be applied to a substrate by melting the composition and then using conventional hot melt adhesive application equipment recognized in the art. Suitable substrates include textile fabric, paper, glass, plastic and metal. Typically, about 5 to 50 g/m2 of adhesive composition is applied to a substrate. The adhesive composition is broadly useful as a hot melt adhesive for those applications where hot melt adhesives are currently employed. The present invention provides that the melting point of the rosin ester tackifier can be selected to suit the end-use for the adhesive composition is intended.
The rosin ester of the present invention does not show large changes in color when subjected to storage conditions at elevated temperature over extended periods of time. The rosin esters so formed will have good color stability at elevated temperature, and hot melt adhesives made from them will have good viscosity stability with little or no skinning. Upon heating, an acceptable rosin ester will exhibit minimal increase in coloration. A rosin ester according to the inventive process will show little or no skinning when mixed with an adhesive polymer, e.g., PETROLITE BE SQUARE(trademark) 185 or ELVAX(trademark) 250 ethylene vinyl acetate (Du Pont, Wilmington, Del.), and heat aged at 176xc2x0 C. for 96 hours.
The process of the present invention provides esters of rosin having light-color and good color stability, with a minimum of labor and cost. The rosin esters of the invention are thus well-suited for use as tackifiers and in other applications where light-colored, color stable rosin esters are needed or desired. The rosin esters of the invention are particularly well suited for hot-melt adhesive tackifiers and pressure sensitive adhesive tackifiers because they display good color stability at elevated temperature, with little or no adhesive skinning, and an acceptable change in adhesive viscosity.
In a general process to prepare rosin esters according to the invention, rosin is charged to a reaction vessel under an inert, i.e., non-oxidizing atmosphere, typically nitrogen, and heated to a temperature of about 160xc2x0 C.-195xc2x0 C. Since the rosin ester has a light-color, and color is sensitive to oxygen exposure, the reaction is preferably conducted under an inert atmosphere to minimize such oxygen exposure. A small amount of a reaction rate enhancer and/or other additive such as a stabilization agent as described above, is then added, along with the polyol. Heating is continued, typically to a temperature of about 240-280xc2x0 C., with concomitant collection of water which is formed by the esterification reaction.
The progress of the reaction may be monitored by periodically pulling samples and measuring the acid number of the samples. Techniques to measure an acid number are well known in the art and need not be described here. See, e.g., ASTM D-465 (1982). Typically, a 12 hour reaction time at 270-280xc2x0 C. can provide a rosin ester having an acid number of about 10.
Once the acid number of the product mixture has reached about 50, preferably about 25, the reaction vessel may be vacuum evacuated to a pressure of about 10-50 mbar at a preferred temperature of 275xc2x0 C. or slightly above. Simultaneously, an inert gas, preferably steam or nitrogen, may be injected into the molten rosin ester. These xe2x80x9cstrippingxe2x80x9d conditions are maintained until the acid number of the product mixture reaches the desired target. The use of vacuum, nitrogen or steam sparging and a temperature of about 275xc2x0 C. or higher provides for the removal of volatile rosin materials, such as decarboxylated rosin. These volatile materials are desirably removed so as to achieve the target softening point for the resin, and also because they tend to adversely affect the odor, color and color stability of the rosin ester product.
As an alternative preferred process, rosin is charged to a reaction vessel under an inert, i.e., non-oxidizing atmosphere, typically nitrogen, and heated to a temperature of about 140xc2x0 C.-170xc2x0 C. Then a small amount of phosphonate salt as defined above, and preferably calcium bismonoethyl(3,5-di-tert-butyl-4-hydroxy-benzyl)-phosphonate, is added to the molten rosin. The preferred phosphonate salt is IRGANOX(trademark) 1425. Approximately 0.1 wt % to about 0.5 wt %, and preferably about 0.15 wt % to about 0.25 wt % of phosphonate salt is added to the rosin.
Either before, simultaneous with, or soon after adding the phosphonate salt to the rosin, a phenol sulfide compound may also be added to the rosin. Preferably, the phenol sulfide compound is added immediately before addition of the phosphonate salt, and the phenol sulfide compound has the formula given above. A preferred phenol sulfide compound is amylphenol disulfide polymer (e.g., VULTAC(trademark) 2 as described above), and is added to the reaction mixture in an amount of about 0.05 wt % to about 0.5 wt % (based on the total weight of rosin and polyol). Next added to the molten rosin is the polyol.
Phosphite esters/derivatives can be added to the esterification reaction mixture in order to help reduce the ester color. An example of a suitable arylphosphite is tris(nonylphenyl)phosphite. One or more of these materials may be added either before, simultaneous with, or after, adding the phenol sulfide compound to the reaction mixture.
The combination of phosphite ester and phosphonate salt may be used regardless of whether the rosin or the polyol is in equivalent excess, or indeed even when the equivalents of rosin equals the equivalents of polyol.
Phosphite ester addition to a forming rosin ester is preferably done after the charging of the rosin. After addition of the phosphite ester, the rosin esterification reaction is allowed to proceed until the acid number of the product mixture reaches about 50 to 25. Then the reaction vessel is placed under vacuum to a pressure of about 10-50 mbar, while injecting an inert gas, preferably nitrogen or steam, into the molten it rosin ester, as described previously. These xe2x80x9cstrippingxe2x80x9d conditions are maintained until the acid number reaches the desired target, which for rosin esters to be used as tackifiers, is about 5 to 15.
The rosin esters of the present invention may find commercial use as tackifiers for packaging adhesives, bookbinding adhesives, furniture adhesives, textile adhesives, wood bonding adhesives, disposable (nonwoven) adhesives, automotive adhesives, appliance adhesives, footwear adhesives, pressure sensitive adhesives and construction adhesives, and in cosmetic formulations, among other uses.
The rosin esters of the present invention, prepared from polyols having hydroxyl functionality separated by at least four carbon atoms, and preferably by at least six carbon atoms, are surprisingly light in color, compared to rosin esters prepared from polyols with hydroxyl groups separated by less than four carbon atoms. In addition to having light color, they also provide other surprising advantages. For instance, they have surprisingly low odor. They also may be formulated into adhesive compositions and, because they typically have low softening points, the adhesive compositions may be prepared and used at relatively low temperature. Such low temperatures are typically desirable because adhesives will oxidize and degrade less at a lower temperature. Although the rosin esters of the of the invention may have low softening points, they still can be used in an adhesive formulations that demonstrate excellent adhesive properties, even at elevated temperature, which is a surprising result. Furthermore, they provide a low softening point material that has superior performance in many respects to a blend of rosin esters that has a composition designed to provide the same low softening point.
When prepared from linear diols, which are a preferred polyol from which to prepare rosin esters of the present invention, they are midblock specific (in styrenic block copolymers) while retaining some polarity for adhesion to low surface energy substrates. They are compatible with many different polymers, which cannot be said for liquid C5 hydrocarbon resins. They give an excellent balance between adhesion and cohesion in hot melt PSA formulations. Also, they afford lower room temperature viscosities than typical commercial competitive resins, such as WINGTACK(trademark) 10 aliphatic C-5 petroleum hydrocarbon resin (Goodyear, Akron, Ohio.).
When prepared from cycloaliphatic diols, (e.g., 1,4-cyclohexanedimethanol) which are another preferred polyol from which to prepare rosin ester of the present invention, the resulting rosin esters are surprisingly light in color and have surprisingly low odor. These rosin esters also demonstrate midblock specificity in styrenic block copolymers, as seen by less migration of the tackifier in an adhesive formulation. They provide adhesion characteristics in pressure sensitive adhesives (PSA""s) comparable to other rosin esters while retaining low odor and color. Cycloaliphatic rosin esters have demonstrated good compatibility with a wide range of polymers. In combination with ethylene n-butyl acrylate polymers (EnBA); they provide adhesives with higher than expected heat resistance, as seen by the rheological crossover point of the formulated adhesive, in comparison with resins having twice the softening point. These resin also offers a lower Tg (per rheological measurements) than prior art resins. Due to this difference between the Tg and crossover point, the formulator will be able to make low application temperature adhesives with good open time and high cohesive strength.
The invention will now be illustrated in more detail by the following non-limiting examples, which demonstrate the advantageous properties of the present invention. Parts and percentages are by weight unless indicated otherwise.
Tall oil rosin (CAS# 8050-09-7) was used in the Examples. Unless otherwise indicated, reagents are of standard commercial grade as obtained from chemical supply houses (e.g., Aldrich Chemical, Milwaukee, Wis.). VULTAC(trademark) 2, which is an amylphenol disulfide polymer (CAS# 68555-986), was obtained from Elf Atochem North America, Inc., Philadelphia, Pa. (this same phenol sulfide may be obtained and used as a solution in other solvents, and could be used in solvent-free form). IRGANOX(trademark) 1425 catalyst (CAS# 65140-91-2), which is calcium bis(monoethyl(3,5-di-tert-butyl-4-hydroxybenzyl)phosphonate), was obtained from Ciba Specialty Chemicals (Tarrytown, N.Y.). HERCOLYN(trademark) D refers to the methyl ester of hydrogenated wood rosin, as supplied by Hercules (Wilmington, Del.; website=herc.com); KRATON(trademark) 1107 refers to a styrene isoprene styrene linear block copolymer having 14% styrene residues and 86% isoprene residues (weight basis) obtained from Shell Chemical (Houston, Tex.); and WINGTAC(trademark) 95 refers to a C5 (i.e., isoprene-based) aliphatic petroleum hydrocarbon resin having a 95-101xc2x0 C. Ring and Ball softening point from Goodyear (Akron, Ohio). UNI-TAC(trademark) XL-10, UNI-TAC(trademark) R85, UNI-TAC(trademark) R85 LT are all rosin (tall oil rosin) esters from Union Camp Corporation (now Arizona Chemical Company, Jacksonville, Fla.) where UNI-TAC(trademark) R85 refers to a glycerol ester of tall oil rosin having a softening point of about 85xc2x0 C., UNI-TAC(trademark) R85 LT refers to a version of UNI-TAC(trademark) R85 having hydrogenated rosin residues, and UNI-TAC(trademark) R 100LT refers to a tall oil rosin ester of pentaerythritol having hydrogenated rosin residues, and UNI-TAC(trademark) XL-10 is a rosin ester that is a clear viscous liquid. NIREZ(trademark) 2040 is a terpene phenolic resin having a softening point of about 120xc2x0 C. available from Arizona Chemical Company (Jacksonville, Fla.). ELVAX(trademark) 220 is an ethylene vinyl acetate copolymer having a melt index of 134-168 g/10 min and a vinyl acetate content of 28% from du Pont (Wilmington, Del.). PETROLIE BE SQUARE(trademark) 185 is a microcrystalline wax having a softening point of 185xc2x0 F. from Petrolite (now part of Baker Petrolite of Sugar Land, Tex., in turn a part of Baker Hughes website=bakerhughes.com). EnBA is an abbreviation for ethylene n-butyl acrylate copolymer, where XW 23. AH is a product designation for a member of the ENABLE(trademark) class of EnBA resins from Exxon Chemical Company (Houston, Tex.). ESCOREZ(trademark) 5600 is a hydrogenated petroleum-based aromatic hydrocarbon tackifier resin having a softening point of 103xc2x0 C. from Exxon Chemical Company (Houston, Tex.).
Suitable stabilizers, which may be present in up to about 1 wt % based on the weight of rosin ester, include one or more of IRGANOX(trademark) 565 (CAS# 991-84-4), which is 4-(4,6-bis(octylthio)-s-triazin-2-yl)amino-2,6-di-tert-butylphenol, IRGANOX(trademark) 1010 (CAS 6683-19-8) which is tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate))methal or IRGANOX(trademark) 1520 (CAS 110553-27-0) which is 2-methyl-4,6-bis{(octylthio)methyl}phenol were obtained from Ciba Specialty Chemicals (Tarrytown, N.Y.). ULTRANOX(trademark) 257, which is the reaction products of 4-methylphenol with dicyclopentadiene and isobutylene (CAS# 68610-51-5) and ULTRANOX(trademark) 236 (CAS 96-69-5) which is 4,4xe2x80x2-thio-bis-(2-tertiary-butyl-5-methylphenol) were obtained from GE Specialty Chemicals, Parkersburg, W.Va. WESTON(trademark) 618 stabilizer, which is distearyl pentaerythritol diphosphite (CAS# 3806-34-6) was obtained from GE Specialty Chemicals, Morgantown, W.Va.
In the following examples, regarding reactant stoichiometry, the term xe2x80x9cequivalent excessxe2x80x9d is used, and is intended to have its standard meaning as employed in the art. However, for additional clarity, it is noted that equivalents refer to the number of reactive groups present in a molar quantity of a molecule. Thus, a mole of a monocarboxylic acid (e.g., rosin) has one equivalent of carboxylic acid, a mole of diol (e.g., 1,4-cyclohexanedimethanol) has two equivalents of hydroxyl. A 10% equivalent excess of rosin refers to the fact that 1.1 moles of carboxylic acid groups from rosin are present in the reaction mixture for every 1.0 moles of hydroxyl groups from polyol.
The term xe2x80x9cANxe2x80x9d refers to acid number, and may be measured by techniques well known in the art. See, e.g., ASTM D-465 (1982). The term xe2x80x9cgsmxe2x80x9d refers to grams per square meter. Softening points were measured with a Mettler FP80 Central Processor and a Mettler FP83 HT Dropping point cell with a softening point ring, and are reported below in degrees centigrade.
For greater accuracy, Gardner colors and values were measured on a Spectronic 301 spectrophotometer (Milton Roy, Rochester, N.Y.) set in the absorbance (Abs) mode. The Gardner values are a digital version of the Gardner colors. For example, a Gardner color of 3- is equivalent to a Gardner value to 2.50 to 2.82; and a Gardner color of 3 is equivalent to a Gardner value of 2.83 to 3.17; and a Gardner color of 3+ is equivalent to a Gardner value of 3.17 to 3.49. The Spectronic 301 is a single beam, visible range spectrophotometer that is microprocessor controlled. The wavelength range is 325 to 900 nm with an accuracy of +/xe2x88x922 nm and wavelength precision of +/xe2x88x921 nm. The Spectronic 301 has a photometric range of xe2x88x920.1 to 2.5 Abs units. The Spectronic 301 requires a thirty minute warmup to maintain these ranges accurately and is calibrated annually using Milton Roy Spectronic standards. Wavelength and photometric data were sent to an external computer by a built-in RS-232C port. The external computer interprets the data, absorbance at wavelengths 200 nm to 700 nm in increments of 10 nm based upon the Gardner colors standards. The data is translated using ASTM standard E308 and provides a printout of both Gardner colors and values. The software is available from Paul N. Gardner Company Inc (Pompano Beach, Fla.).
Rheological measurements were performed on a TA Instruments TA Rheolyst 1000-N (New Castle, Del.) operated with the following parameters when used to obtain rheological curves useful to identify, e.g., cross-over points: Geometryxe2x80x944 cm parallel plate; Gapxe2x80x941000 microns; Frequencyxe2x80x946.28 rads/sec; Temperature range =xe2x88x9220 C to 150 C; Ramp ratexe2x80x943 degree""s per minute from 150 C to xe2x88x9220 C; Strainxe2x80x9410% constant.
In the following examples, ESCOREZ(trademark) 5600, UNI-TAC(trademark) R85 LT, UNI-TAC(trademark) R 100 LT, UNI-TAC(trademark) XL-10, WINGTAC(trademark) 10, WINGTAC(trademark) 95, and NIREZ(trademark) 2040 are each trademarks for tackifiers. SHELLFLEX(trademark) 371 and HERCOLYN(trademark) D are each trademarks for hydrocarbon oils. KRATON(trademark) 1107 is a trademark for a thermoplastic rubber and IRGANOX(trademark) 1010 is a trademark for an antioxidant.